1. Field of the invention:
This invention relates to an apparatus for the formation of images in which a photosensitive sheet coated with pressure-rupturable capsules is first transported through a light-exposure section to be exposed to light to obtain a latent image and then temporarily stored in a buffer section, and finally transported together with an image-receiving sheet through a pressure-transfer section to be pressurized to obtain a colored image on said image-receiving sheet, and more particularly relates to an apparatus for the formation of images in which pressure-rupturable capsules on said photosensitive sheet are prevented from rupturing when the photosensitive sheet is transported alone without said image-receiving sheet through said pressure-transfer section.
2. Description of the prior art:
An apparatus for the formation of images in which a photosensitive sheet coated with pressure-rupturable capsules containing chromogenic materials is first exposed to light to obtain a latent image and then is pressed against an image-receiving sheet coated with developing materials to obtain a colored image on the image-receiving sheet has been proposed by, for example, Japanese Laid-Open Patent Publication No. 58-88739.
The image-forming process in such an apparatus comprises two steps; a light-exposure step and a pressure-transfer step. In the light-exposure step, the photosensitive sheet, one side of which is coated with pressure-rupturable capsules containing chromogenic materials that are hardened when exposed to light, is first transported into a light-exposure section, where it is exposed to light reflected from an original. The light reflected from the original selectively illuminates the pressure-rupturable capsules on the photosensitive sheet so that some of the capsules receive the light and become hardened and the others do not receive the light and are left unchanged, resulting in a latent image corresponding to the image of the original. Then, in the pressure-transfer step, the photosensitive sheet on which the latent image has been formed is transported into the pressure-transfer section, where the photosensitive sheet is placed together with the image-receiving sheet and pressure is applied thereto. Thus, the pressure-rupturable capsules that have not been hardened rupture, allowing the chromogenic materials contained therein to flow out onto the image-receiving sheet. Then, the chromogenic materials react with the developing materials coated on the image-receiving sheet, which gives rise to color in the chromogenic materials, resulting in a colored image corresponding to the latent image on the image-receiving sheet. In general, the pressure-transfer section consists of a pair of pressure rollers, between which the photosensitive sheet and the image-receiving sheet are supplied at the same time to be pressurized.
In the light-exposure step mentioned above, the speed at which the photosensitive sheet is transported through the light-exposure section determines the light-exposure time, which in turn determines the degree to which the capsules are hardened. This influences the quality of a latent image to be formed on the photosensitive sheet. Similarly, in the pressure-transfer step mentioned above, the speed at which the photosensitive sheet is transported through the pressure-transfer section determines the time of the reaction between the chromogenic materials and the developing materials. The reaction time influences the quality of a colored image to be formed on the image-receiving sheet. In order to obtain a distinct colored image, the photosensitive sheet should be transported through the light-exposure section at the optimum speed (hereinafter referred to as "the optimum light-exposure speed") so that a latent image can be properly formed with the optimum light-exposure time, and then should be transported through the pressure-transfer section at the optimum speed (hereinafter referred to as "the optimum pressure-transfer speed") so that a colored image can be properly formed with the optimum reaction time. In general, the optimum light-exposure speed is different from the optimum pressure-transfer speed. If the photosensitive sheet is continuously transported through the light-exposure section and the pressure-transfer section, it can only be transported at the same speed through those two sections. Thus, the sheet-transporting speed cannot be set at the respective optimum level for each section, and a distinct colored image cannot be obtained.
To solve the above-mentioned problem, an apparatus for the formation of images has been proposed by, for example, Japanese Patent Application No. 63-64426 in which the photosensitive sheet is first transported from the roll of the sheet through the light-exposure section to a buffer section at the optimum light-exposure speed and temporarily stays at the buffer section between the light-exposure section and the pressure-transfer section, and is finally transported from the buffer section into the pressure-transfer section at the optimum pressure-transfer speed.
In such an apparatus, the sheet-transportation speed can be set at respective optimum levels for the light-exposure section and the pressure-transfer section, as mentioned above. This makes it possible to properly form a latent image on the photosensitive sheet and a distinct colored image on the image-receiving sheet.
The buffer section mentioned above generally comprises a buffer roller which usually stays at its base position between the light-exposure section and the pressure transfer section. The buffer roller moves from the base position into a position away from the pressure-transfer section at the time of the light-exposure step, and comes back to the base position at the time of the pressure-transfer step. With this movement of the buffer roller, the photosensitive sheet is transported through the light-exposure section at the optimum light-exposure speed and then transported through the pressure-transfer section at the optimum pressure-transfer speed.
Such an apparatus, however, is sometimes jammed by an image-receiving sheet at the time of the pressure-transfer step. When the jamming occurs, the operation of the apparatus is suspended with its main motor stopped so that the jammed sheet is removed from the body of the apparatus. Since the light-exposure step has been completed, the portion of the photosensitive sheet corresponding to the latent image is located at the buffer section. Thus, after the image-receiving sheet is removed, this portion of the photosensitive sheet should be transported from the buffer section through the pressure-transfer section to be wound around a take up rod so that the whole apparatus is ready for the next image-forming process. When the portion of the photosensitive sheet corresponding to the latent image is transported through the pressure-transfer section to be pressurized alone without the image-receiving sheet, the pressure-rupturable capsules that are not hardened are pressurized to rupture, allowing the chromogenic materials therein to flow out onto the pressure rollers and/or other components within the body of the apparatus. This causes the pressure rollers and/or the inside of the body of the apparatus to be stained with the chromogenic materials. Moreover, when another image-receiving sheet is transported into the pressure rollers at the time of the next image-forming process, the chromogenic materials that have flown onto the pressure rollers may adhere to the back of the sheet.